eRuby - no implicit conversion of nil into String when comparing numbers in an if statement

I have a basic eRuby each loop

 <% @product_images.each do |image|%>

        <% if @counter < 4 %>

           <% p 'Im in here' %>
        <% else %>

           <% return %>
        <% end %>

          <% @counter += 1 %>
          <% p @counter %>

 <% end %>

Inside my loop i have an if statement that checks if @counter is < than 4.

Controller code

def show

     productId = params[:id]

     @product_images = ProductImage.where("product_id = ?", productId)

     @counter = 0
end

When i run this code it should return once the counter is greater than 4 but i get an error that says no implicit conversion of nil into String

This is pretty straight forward code i can't seem to figure out what i'm doing wrong. It seems like it's breaking in the line

<% if @counter < 4 %>

Here is a picture of the error:

It looks like you are trying to limit the number of @product_images that are rendered in your view. Instead of using @counter, you should simply limit the number of @product_images in your controller, something like:

def show
  @product = Product.find_by(id: params[:id])
  @product_images = @product.product_images.limit(4)
end

And then in your view, do something like:

<% @product_images.each do |image| %>
  # do stuff
<% end %>

This, naturally, assumes that:

class Product < ActiveRecord::Base 
  has_many :product_images
end

And:

class ProductImage < ActiveRecord::Base
  belongs_to :product
end

You could put that logic back in the view, like:

<% @product.product_images.limit(4).each do |image| %>
  # do stuff
<% end %>

And then your show action could be just:

def show
  @product = Product.find_by(id: params[:id])
end

But, I prefer leaving it in the controller to reduce the coupling between your views and your models.